As everyone knows, the Black family (and apparently a few others) are named after stars. Sirius, Regulus, Bellatrix, Narcissa, Andromeda, everyone. If you're going to be playing one of the Blacks and need a middle name (or are playing a parents and need a first and middle), or even if you just think star names are a good idea and are seeking one for your OC, go here, it's a list of tons and tons of star names.
And for whoever takes Regulus, let it be known that your and Sirius's parents are, by Sirius's profile, named Cursa and Mirach. *nod*